JP2005173468A - Positive resist composition and resist pattern forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive resist composition which reduces LER and is excellent in resolution and a resist pattern forming method using the resist composition. <P>SOLUTION: The positive resist composition contains (A) a copolymer including a constitutional unit (a1) derived from a (meth)acrylic ester containing a polycyclic-group-containing acid-dissociable dissolution inhibiting group, a constitutional unit (a2) derived from a (meth)acrylic ester containing a lactone-containing monocyclic or polycyclic group, a constitutional unit (a3) derived from a (meth)acrylic ester containing a hydroxyl-containing polycyclic group, and a constitutional unit (a4) derived from a (meth)acrylic ester containing a polycyclic-group-containing non-acid-dissociable dissolution inhibiting group, other than the constitutional units (a2) and (a3), as a resin component whose alkali solubility is increased by the action of an acid; and (B) at least one sulfonium compound represented by formula (b-1) or (b-2) as an acid generator component which generates an acid upon exposure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a positive resist composition and a resist pattern forming method.

In recent years, in the manufacture of semiconductor elements and liquid crystal display elements, miniaturization has rapidly progressed due to advances in lithography technology. As a technique for miniaturization, the wavelength of an exposure light source is generally shortened. Specifically, conventionally, ultraviolet rays typified by g-line and i-line have been used, but now KrF excimer laser (248 nm) has been introduced.
In addition, as one of the resist materials that satisfy the high resolution conditions that can reproduce patterns with fine dimensions, it contains a base resin that increases alkali solubility by the action of acid and an acid generator that generates acid upon exposure. A chemically amplified positive resist composition is known.
Currently, onium salts are most commonly used as acid generators. The anion portion (acid) of the onium salt is mostly a chain fluorinated alkyl sulfonate ion, and other acids are rarely used due to the problem of acidity. As the alkyl chain of the fluorinated alkyl, in order to control the diffusion length of the acid in the resist film, those having a long carbon number are preferred. However, the alkyl chain is a fluorinated alkyl sulfone having a carbon number of 4 or more. With regard to acids, questions about safety have begun to be pointed out, and their use is currently limited worldwide. Therefore, there is a need for an acid generator having a short diffusion length in a resist film without using such a long-chain fluorinated alkylsulfonic acid.

On the other hand, with the rapid miniaturization of semiconductor elements in recent years, further improvement in resolution is required. In particular, in the formation of so-called isolated line patterns in which the ratio of the resist line portion size to the space portion size is less than 1, for example, the ratio of the resist line portion size to the space portion size is 1/9, it is necessary to improve the resolution. It has become.
Further, such an isolated line pattern portion (sparse pattern portion) and the ratio of the resist line portion size to the space portion size is 1 or more, for example, the ratio of the resist line portion size to the space portion size is 1/1. In a sparse / dense mixed pattern forming process in which so-called line and space (L & S) pattern portions (dense pattern portions) coexist, there arises a so-called proximity effect problem in which there is a difference in resist pattern size between the sparse pattern portion and the dense pattern portion. However, it is difficult to suppress such a proximity effect with a conventional resist, and an improvement is desired.
Further, along with the rapid miniaturization of semiconductor elements, line edge roughness (LER) has become a serious problem, and improvement thereof is also desired.

The present applicant has already included (meth) acrylic acid containing a specific quaternary copolymer as a chemically amplified positive resist composition that is excellent in the resolution of isolated line patterns and can suppress the proximity effect in densely mixed patterns. A positive resist composition has been proposed in which a resin component having a unit derived from an ester in the main chain and having increased solubility in alkali by the action of an acid is used as a base resin (see Patent Document 1).
However, although the positive resist composition containing the quaternary copolymer described in Patent Document 1 is excellent in the resolution of the isolated line pattern, the resolution of the L & S pattern, the trench pattern, that is, the resist The resolution of an isolated space pattern in which the ratio of the space part size to the line part size is less than 1, for example, the ratio of the space part size to the resist line part size is 1/9 is not sufficient. Therefore, further improvement is required for the resolution of these patterns. Further, in the positive resist composition containing the quaternary copolymer, further improvement in line edge roughness is required.
JP 2003-167347 A

  The present invention has been made in view of the above circumstances, and uses a positive resist composition excellent in LER reduction and resolution, particularly in the resolution of an L & S pattern and an isolated space pattern, and the resist composition. It is an object of the present invention to provide a resist pattern forming method.

As a result of intensive studies, the present inventors have found that the above problem can be solved by using the quaternary copolymer and a specific acid generator in combination.
The present invention has been made on the basis of the above findings. The first invention of the present invention is (A) a resin component whose alkali solubility is increased by the action of an acid, and (B) an acid that generates an acid by exposure. A positive resist composition containing a generator component,
The resin component (A) is a structural unit (a1) derived from a (meth) acrylate ester containing a monocyclic or polycyclic group-containing acid dissociable, dissolution inhibiting group, a lactone-containing monocyclic or polycyclic group A structural unit (a2) derived from a (meth) acrylic acid ester containing, a structural unit (a3) derived from a (meth) acrylic acid ester containing a hydroxyl group-containing polycyclic group, and the structural unit (a2), A copolymer containing a structural unit (a4) derived from a (meth) acrylic acid ester containing a polycyclic group-containing non-acid dissociable, dissolution inhibiting group other than (a3),
The acid generator component (B) is represented by the following general formula (b-1) or (b-2)

[Wherein X represents an alkylene group having 2 to 6 carbon atoms in which at least one hydrogen atom is substituted with a fluorine atom; Y and Z each independently represents at least one hydrogen atom substituted with a fluorine atom; R ^{1 to} R ³ each independently represents an aryl group or an alkyl group, and at least one of R ^{1 to} R ³ represents an aryl group]
A positive resist composition comprising at least one sulfonium compound represented by the formula:
According to a second aspect of the present invention, a resist film is formed on a substrate using the positive resist composition, the resist film is selectively exposed, and then developed with an alkali. A resist pattern forming method characterized in that a pattern is formed.

  In the present invention, the “lactone-containing monocyclic group or polycyclic group” is a monocyclic group consisting of a lactone ring or a polycyclic group having a lactone ring. At this time, the lactone ring refers to one ring containing a —CO—O— structure, and this is counted as the first ring. Therefore, here, in the case of only the lactone ring, the lactone-containing monocyclic group is used, and in the case of having another ring structure, the lactone-containing polycyclic group is used regardless of the structure. In the present invention, the “structural unit” means a monomer unit constituting the polymer. In addition, the “structural unit derived from (meth) acrylic acid ester” in this specification is derived from an acrylic acid ester in which R is a hydrogen atom in the unit represented by the following general formula (5). A structural unit derived from a methacrylic acid ester in which R is a methyl group, and further R is a lower alkyl group of about C2 to C5, specifically an ethyl group, a propyl group, an isopropyl group, n-butyl. A general term for a structural unit which is a linear or branched alkyl group such as a group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, and a neopentyl group.

  According to the positive resist composition and the resist pattern forming method of the present invention, it is possible to form a resist pattern excellent in LER reduction and resolution, in particular, the resolution of L & S pattern and isolated space pattern.

Hereinafter, the present invention will be described in more detail.
≪Positive resist composition≫
The positive resist composition of the present invention comprises a resin component (A) whose alkali solubility is increased by the action of an acid (hereinafter, also referred to as component (A)), and an acid generator component that generates an acid upon exposure ( B) (hereinafter also referred to as component (B)).
In the present invention, the component (A) is a copolymer containing the structural units (a1) to (a4), and the component (B) is the general formula (b-1) or (b-2). It contains at least one kind of sulfonium compound represented by the following.
By combining these (A) component and (B) component, it is possible to form a resist pattern having excellent resolution, particularly, L & S pattern and isolated space pattern resolution. Moreover, the shape of the obtained resist pattern is also excellent in the rectangularity with high verticality of the pattern side wall. Furthermore, a resist pattern with reduced line edge roughness (LER) can be formed. Also, the depth of focus (DOF) when forming the resist pattern is large. Here, LER means, for example, uneven unevenness formed on the side wall of the line and space pattern in the developed resist pattern.

<(A) component>
The component (A) is an alkali-insoluble one having a so-called acid dissociable, dissolution inhibiting group, and when an acid generated from the component (B) is acted upon by exposure, the acid dissociable, dissolution inhibiting group is dissociated. A) The whole component changes from alkali-insoluble to alkali-soluble. Therefore, when exposure is performed through a mask pattern in the formation of a resist pattern, or when post-exposure heating (PEB) is performed in addition to exposure, the exposed portion turns into alkali-soluble, while the unexposed portion remains alkali-insoluble. Therefore, a positive resist pattern can be formed by alkali development.

The structural unit (a1) is a unit derived from a (meth) acrylic acid ester containing a monocyclic or polycyclic group-containing acid dissociable, dissolution inhibiting group.
Examples of the monocyclic group include a group obtained by removing one hydrogen atom from a cycloalkane, for example, an aliphatic monocyclic group such as a cyclohexyl group. Examples of polycyclic groups include bicycloalkanes, tricycloalkanes, teracycloalkanes, etc., groups obtained by removing one hydrogen atom from polycycloalkanes such as adamantane, norbornane, isobornane, tricyclodecane, and tetracyclododecane. An aliphatic polycyclic group is mentioned. Here, many of these monocyclic groups or polycyclic groups have been proposed in ArF resists, and in the present invention, these monocyclic groups or polycyclic groups can be arbitrarily selected and used. However, it is preferable to use an aliphatic polycyclic group such as an adamantyl group, a norbornyl group, or a tetracyclododecanyl group from the viewpoint of industrial availability.

As described above, the acid dissociable, dissolution inhibiting group has an alkali dissolution inhibiting property that makes the entire component (A) insoluble in alkali before exposure, and the action of an acid generated from the component (B) described later after exposure. To dissociate the entire component (A) into alkali-soluble.
As such acid dissociable, dissolution inhibiting groups, for example, those that form a cyclic or chain tertiary alkyl ester with a carboxyl group of (meth) acrylic acid are widely known.
As the structural unit (a1), any unit can be used without particular limitation as long as it has the functions described above. Specifically, at least one structural unit selected from the following general formula (1), (2), or (3) is preferable in that it has excellent resolution and dry etching resistance.

（式中、Ｒは水素原子または低級アルキル基、Ｒ^１は低級アルキル基である）

(Wherein R is a hydrogen atom or a lower alkyl group, and R ¹ is a lower alkyl group)

（式中、Ｒは水素原子または低級アルキル基、Ｒ^２およびＲ^３はそれぞれ独立して低級アルキル基である）

(Wherein R is a hydrogen atom or a lower alkyl group, and R ² and R ³ are each independently a lower alkyl group)

（式中、Ｒは水素原子または低級アルキル基、Ｒ^４は第３級アルキル基である）

(Wherein R is a hydrogen atom or a lower alkyl group, and R ⁴ is a tertiary alkyl group)

The structural unit represented by the general formula (1) is a tertiary alkyl group on a ring skeleton such as an adamantyl group in which the carbon atom adjacent to the oxygen atom (—O—) of the ester portion of (meth) acrylic acid is This is the case.
R is a hydrogen atom or a methyl group, and further a lower alkyl group of about C2 to C5, specifically an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, Examples include lower linear or branched alkyl groups such as isopentyl group and neopentyl group.
R ¹ is a lower linear or branched group such as a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, or a neopentyl group. Of the alkyl group. Here, if R ¹ is an alkyl group having 2 or more carbon atoms, the acid dissociation tends to be higher than that of a methyl group, which is preferable. However, industrially, a methyl group or an ethyl group is most preferable.

In the structural unit represented by the general formula (2), the carbon atom adjacent to the oxygen atom (—O—) of the ester portion of (meth) acrylic acid is a tertiary alkyl group, and further adamantyl is contained in the alkyl group. This is the case when a ring skeleton such as a group is present. In the structural unit represented by the general formula (2), R has the same definition as in the general formula (1), and R ² and R ³ are independent lower alkyl groups, that is, about the above-described C1 to C5. These are linear or branched alkyl groups. Such groups tend to be more acid dissociable than 2-methyl-2-adamantyl groups. In addition, it is industrially preferable that R ² and R ³ are both methyl groups.

The structural unit represented by the general formula (3) is not a (meth) acrylic ester part, but a carbon atom adjacent to an oxygen atom (—O—) of another ester part is a tertiary alkyl group, This is a case where the ester part and the (meth) acrylic acid ester part are connected by a ring skeleton such as a tetracyclododecanyl group. In the unit represented by the general formula (3), R has the same definition as in the general formula (1), and R ⁴ is a tertiary alkyl group such as a tert-butyl group or a tert-amyl group. . As for ^{R 4} is, to an tert- butyl group is preferred industrially.
Among the structural units represented by the general formulas (1) to (3), particularly, the structural unit represented by the general formula (1), and R ¹ is a methyl group or an ethyl group However, it is preferable in terms of excellent resolution.

The structural unit (a2) is a structural unit derived from a (meth) acrylic acid ester containing a lactone-containing monocyclic or polycyclic group. The lactone functional group is effective in increasing the adhesion of the resist film formed from the composition of the present invention to the substrate or increasing the hydrophilicity with the developer.
As the structural unit (a2), any unit can be used without particular limitation as long as it has both such a lactone functional group and a cyclic group. Specifically, examples of the lactone-containing monocyclic group include groups obtained by removing one hydrogen atom from γ-butyrolactone, and examples of the lactone-containing polycyclic group include bicycloalkanes having a lactone group, tricyclo groups. Examples include groups in which one hydrogen atom has been removed from an alkane or tetracycloalkane. In particular, a lactone-containing bicycloalkane having the following structural formula (6) or a group obtained by removing one hydrogen atom from a lactone-containing tricycloalkane having the structural formula (7) is easily available industrially. This is advantageous.

  Specific examples of the structural unit (a2) include structural units derived from (meth) acrylic acid esters containing a lactone-containing monocycloalkyl group or tricycloalkyl group, and more specifically, Examples include structural units represented by formulas (8) to (10).

（式中、Ｒは水素原子または低級アルキル基である）

(Wherein R is a hydrogen atom or a lower alkyl group)

結合位置が５位又は６位の異性体の混合物として存在する。
（式中、Ｒは水素原子または低級アルキル基である）

It exists as a mixture of isomers at the 5-position or 6-position.
(Wherein R is a hydrogen atom or a lower alkyl group)

（式中、Ｒは水素原子または低級アルキル基である）

(Wherein R is a hydrogen atom or a lower alkyl group)

In addition, among the structural units represented by the general formulas (8) to (10), the general formula having an ester bond on the α-carbon (for example, the effect of suppressing and reducing the proximity effect is excellent) ( The structural unit derived from (meth) acrylic acid γ-butyrolactone ester represented by 10), that is, a (meth) acrylic acid ester of γ-butyrolactone is preferred.
Moreover, the norbornane lactone ester of (meth) acrylic acid represented by the general formulas (8) and (9), that is, the structural unit derived from the (meth) acrylic acid ester of norbornane lactone is the shape of the resist pattern to be obtained, For example, it is preferable because the rectangularity is even better. In particular, the structural unit represented by the general formula (9) is preferable because of its extremely high effect.

The structural unit (a3) is a structural unit derived from a (meth) acrylic acid ester containing a hydroxyl group-containing polycyclic group. By having a hydroxyl group that is a polar group, the developer of the resin component (A) as a whole This improves the hydrophilicity of the light and improves the alkali solubility of the exposed portion, thereby contributing to the improvement of the resolution. Here, as the polycyclic group, the same polycyclic group as in the structural unit (a1) can be used.
Such a structural unit (a3) is not particularly limited as long as it is a hydroxyl group-containing polycyclic group, and any unit can be used. Specifically, a hydroxyl group-containing adamantyl group, particularly a structural unit represented by the following general formula (4) is preferable in that it has an effect of increasing dry etching resistance and an effect of making the pattern cross section rectangular.

（式中、Ｒは水素原子または低級アルキル基である）

(Wherein R is a hydrogen atom or a lower alkyl group)

The structural unit (a4) is a structural unit derived from a (meth) acrylic ester containing a polycyclic group-containing non-acid dissociable, dissolution inhibiting group other than the structural units (a2) and (a3).
A structural unit derived from a (meth) acrylic acid ester containing a polycyclic group-containing non-acid dissociable, dissolution inhibiting group is a function of suppressing the alkali solubility by increasing the hydrophobicity of the entire component (A) before and after exposure. Is a structural unit having That is, the alkali solubility of the entire component (A) before exposure is reduced, and the acid dissociable dissolution of the structural unit (a1) is suppressed without being dissociated by the action of an acid generated from the component (B) after exposure. It is a structural unit containing a group having a dissolution inhibitory property that reduces the alkali solubility of the entire component (A) when the entire component (A) is changed to alkali-soluble due to the dissociation of the group within a range that does not become insoluble in alkali.
The structural unit (a4) does not overlap with the structural unit (a1), the structural unit (a2), or the structural unit (a3). That is, none of the groups such as the acid dissociable, dissolution inhibiting group in the structural unit (a1), the lactone group in the structural unit (a2), and the hydroxyl group in the structural unit (a3) are retained.
As the polycyclic group for the structural unit (a4), the same polycyclic groups as those for the structural unit (a1) can be used.
As such a structural unit (a4), many conventionally known ArF positive resist materials can be used, and in particular, tricyclodecanyl (meth) acrylate, adamantyl (meth) acrylate, tetra A structural unit derived from at least one selected from cyclododecanyl (meth) acrylate is preferable in terms of industrial availability. These exemplified structural units are shown below as general formulas (11) to (14). Among these, the structural unit represented by the general formula (11) is preferable because the shape of the obtained resist pattern, for example, rectangularity is particularly good.

結合位置が５位又は６位の異性体の混合物として存在する。
（式中、Ｒは水素原子または低級アルキル基である）

It exists as a mixture of isomers at the 5-position or 6-position.
(Wherein R is a hydrogen atom or a lower alkyl group)

（式中、Ｒは水素原子または低級アルキル基である）

(Wherein R is a hydrogen atom or a lower alkyl group)

（式中、Ｒは水素原子または低級アルキル基である）

(Wherein R is a hydrogen atom or a lower alkyl group)

As the component (A), in particular, the structural unit (a1) includes the structural unit represented by the general formula (1), and the structural unit (a2) includes the structural unit represented by the general formula (9). A copolymer containing the structural unit represented by the general formula (4) as the structural unit (a3) and the structural unit represented by the general formula (11) as the structural unit (a4), that is, the following 4 Copolymers containing seed structural units are preferred. This is because LER and the rectangularity of the resist pattern are particularly excellent. Moreover, since it becomes higher than resin mentioned later about dry etching tolerance, it is preferable.
Especially, the copolymer which consists of structural unit (a1)-(a4) is excellent in the said effect, and preferable.

（式中、Ｒは水素原子または低級アルキル基であり、Ｒ^５はメチル基またはエチル基である）

(In the formula, R is a hydrogen atom or a lower alkyl group, and R ⁵ is a methyl group or an ethyl group)

  (A) About the ratio of each structural unit (a1)-(a4) in a component, structural unit (a1) is 25-50 mol%, Preferably it is the range of 30-40 mol%, and structural unit (a2) Is in the range of 25 to 50 mol%, preferably 30 to 40 mol%, the structural unit (a3) is in the range of 10 to 30 mol%, preferably 10 to 20 mol%, and the structural unit (a4) is 3 It is suitable to be in the range of ˜25 mol%, preferably 5 to 20 mol%. With such a range, the depth of focus of the isolated pattern formed from the obtained positive resist composition can be greatly improved, and the proximity effect can be sufficiently suppressed to greatly reduce this. In addition, if it deviates greatly from the said range, there exists a possibility that the malfunction that resolution may fall may arise.

  Further, in the positive resist composition of the present invention, as the component (A), the dry resisting resistance known as a conventional chemically amplified positive resist is added to the monomer forming each of the structural units (a1) to (a4). Carboxyl having an ethylenic double bond for alkali-solubility such as acrylic acid derivatives, methacrylic acid derivatives, acrylic acid, methacrylic acid, maleic acid, fumaric acid, etc. having etchability improving groups and non-acid dissociable, dissolution inhibiting groups Known monomers and the like used for the production of acid and acrylic resin can be appropriately combined and copolymerized as necessary.

  Examples of acrylic acid derivatives include dry etching resistance to hydroxyl groups of carboxyl groups such as naphthyl acrylate, benzyl acrylate, 3-oxocyclohexyl acrylate, esters of acrylic acid and terpineol, and esters of acrylic acid and 3-bromoacetone. And an acrylic ester protected with a non-acid-dissociable substituent. Examples of methacrylic acid derivatives include methacrylic acid derivatives corresponding to these acrylic acid derivatives.

Examples of the carboxylic acid having an ethylenic double bond include acrylic acid, methacrylic acid, maleic acid, and fumaric acid.
Examples of known monomers used in the production of acrylic resins include, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-hexyl acrylate, acrylic acid Examples thereof include alkyl acrylates such as octyl, 2-ethylhexyl acrylate, lauryl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and the corresponding alkyl methacrylates.

  The component (A) can be obtained by polymerizing a monomer for deriving each structural unit by a known radical polymerization using a radical polymerization initiator such as azobisisobutyronitrile (AIBN).

  The mass average molecular weight of the component (A) (polystyrene conversion standard by gel permeation chromatography) is preferably 7500 or less. More preferably, it is 4000-7200, Most preferably, it is 5000-6500. When the mass average molecular weight is 7500 or less, LER is further improved. Also, development defects during alkali development are reduced. Moreover, the synthesis | combination of (A) component is easy in a mass mean molecular weight being 4000 or more.

  The component (A) can be composed of one kind or two or more kinds of resins. For example, a copolymer composed of the structural units (a1) to (a4) as described above may be used alone, Two or more kinds may be mixed and used.

In the present invention, since the component (A) is a copolymer containing the structural units (a1) to (a4), the depth of focus of the isolated line pattern can be improved and the proximity effect can be reduced. As a result, a resist pattern faithful to the mask pattern is formed in both sparse and dense patterns.
Further, the resolution of the L & S pattern and the isolated space pattern is enhanced by the combination with the component (B) described later. Furthermore, the LER, shape, depth of focus, etc. of these patterns are improved.

<(B) component>
In the present invention, the component (B) contains a sulfonium compound represented by the general formula (b-1) or (b-2) (hereinafter sometimes referred to as a sulfonium compound 1 or a sulfonium compound 2, respectively). It is characterized by this.

In formulas (b-1) and (b-2), X is a linear or branched alkylene group in which at least one hydrogen atom is substituted with a fluorine atom, and the alkylene group has 2 to 2 carbon atoms. 6, preferably 3 to 5, and most preferably 3 carbon atoms.
Y and Z are each independently a linear or branched alkyl group in which at least one hydrogen atom is substituted with a fluorine atom, and the alkyl group has 1 to 10 carbon atoms, preferably 1 to 1 carbon atoms. 7, more preferably 1-3. The smaller the number of carbon atoms of the alkylene group of X or the number of carbon atoms of the alkyl groups of Y and Z, the better the solubility in the resist solvent, which is preferable.
In addition, in the alkylene group of X or the alkyl group of Y and Z, the greater the number of hydrogen atoms substituted by fluorine atoms, the stronger the acid, and the transparency to high energy light and electron beams of 200 nm or less Is preferable. The proportion of fluorine atoms in the alkylene group or alkyl group, that is, the fluorination rate is preferably 70 to 100%, more preferably 90 to 100%, and most preferably all hydrogen atoms are substituted with fluorine atoms. A perfluoroalkylene group or a perfluoroalkyl group.

R ^{1 to} R ³ each independently represents an aryl group or an alkyl group.
At least one of R ^{1 to} R ³ represents an aryl group. Of R ^{1 to} R ³ , two or more are preferably aryl groups, and most preferably R ^{1 to} R ³ are all aryl groups.
The aryl group of R ¹ to R ^3, is not particularly limited, for example, an aryl group having 6 to 20 carbon atoms, an alkyl group, a phenyl group which may not be substituted with a halogen atom or the like And a naphthyl group. An aryl group having 6 to 10 carbon atoms is preferable because it can be synthesized at low cost.
The alkyl group of R ¹ to R ^3, is not particularly limited, for example, a straight, include alkyl groups such as branched or cyclic. It is preferable that it is C1-C5 from the point which is excellent in resolution. Specific examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, an n-pentyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a nonyl group, and a decanyl group. A methyl group is preferable because it is excellent in resolution and can be synthesized at low cost.
Among these, it is most preferable that all of R ^{1 to} R ³ are phenyl groups.

  These sulfonium compounds 1 and 2 may be used alone or in combination of two or more.

  In the present invention, since the component (B) is excellent in LER, resolution, resist pattern shape, depth of focus, etc., it is necessary to contain sulfonium compounds 1 and 2.

  In the component (B), the ratio of at least one selected from the sulfonium compounds 1 and 2 is preferably 25 to 100% by mass, more preferably 30 to 100% by mass, based on the total amount of the component (B). The effect of this invention becomes sufficient because it is 25 mass% or more.

In the present invention, the component (B) may further contain a known acid generator that has been conventionally used in chemically amplified photoresist compositions. Various acid generators have been known such as onium salts such as iodonium salts and sulfonium salts, oxime sulfonates, bisalkyl or bisarylsulfonyldiazomethanes, nitrobenzyl sulfonates, iminosulfonates, and disulfones. Therefore, these known acid generators can be used without particular limitation.
Of these, onium salts containing fluorinated alkyl sulfonate ions as anions (hereinafter referred to as onium salt acid generators) are particularly preferred because the strength of the acid generated is strong.
Examples of the cation of the onium salt acid generator include a lower alkyl group such as a methyl group, an ethyl group, a propyl group, an n-butyl group and a tert-butyl group; a lower alkoxy group such as a methoxy group and an ethoxy group. Preferred are mono- or diphenyliodonium, mono-, di-, or triphenylsulfonium; dimethyl (4-hydroxynaphthyl) sulfonium and the like.
The anion of the onium salt acid generator is a fluorine atom in which part or all of the hydrogen atoms of a linear alkyl group having 1 to 7 carbon atoms, more preferably 1 to 3 carbon atoms are substituted with fluorine atoms. Alkyl sulfonate ions are preferred because of their high safety. When the number of carbon atoms is 7 or less, the strength as a sulfonic acid is increased. Further, the fluorination rate of the fluorinated alkyl sulfonate ion (ratio of fluorine atoms in the alkyl group) is preferably 10 to 100%, more preferably 50 to 100%. Particularly, all the hydrogen atoms are fluorine atoms. The substituted one is preferable because the strength of the acid is increased. Specific examples thereof include trifluoromethane sulfonate and heptafluoropropane sulfonate.

Specific examples of such onium salt acid generators include diphenyliodonium trifluoromethanesulfonate or nonafluorobutanesulfonate, bis (4-tert-butylphenyl) iodonium trifluoromethanesulfonate or nonafluorobutanesulfonate, triphenylsulfonium. Trifluoromethanesulfonate, its heptafluoropropanesulfonate or its nonafluorobutanesulfonate, tri (4-methylphenyl) sulfonium trifluoromethanesulfonate, its heptafluoropropanesulfonate or its nonafluorobutanesulfonate, dimethyl (4-hydroxynaphthyl) sulfonium Trifluoromethanesulfonate, its heptafluoropropanesulfonate Or its nonafluorobutane sulfonate, monophenyldimethylsulfonium trifluoromethane sulfonate, its heptafluoropropane sulfonate or its nonafluorobutane sulfonate, diphenyl monomethylsulfonium trifluoromethane sulfonate, its heptafluoropropane sulfonate or its nonafluorobutane sulfonate, etc. Is mentioned.
These onium salt acid generators can be used singly or in combination of two or more.

  When the onium salt acid generator is used as a component in combination with at least one selected from sulfonium compounds 1 and 2, the proportion of the onium salt acid generator is preferably 10 to 75% by mass. 30 to 70% by mass is more preferable. By blending an onium salt-based acid generator within the above range, an acid generator is excellent in LER and development defects. The mixing ratio (mass ratio) of the onium salt acid generator and at least one selected from sulfonium compounds 1 and 2 is 1: 9 to 9: 1, preferably 1: 5 to 5: 1, and most preferably. Is 1: 2 to 2: 1. By mixing and using an acid generator at the above ratio, the LER and development defects are excellent.

  (B) A component is 0.1-30 mass parts with respect to 100 mass parts of (A) component, Preferably it is 0.5-20 mass parts, More preferably, it is used in the ratio of 1-10 mass parts. If it is less than the lower limit, no image is formed, and if it exceeds 30 parts by mass, it becomes difficult to form a uniform solution and the storage stability may be lowered.

<(C) component>
The positive resist composition of the present invention can be produced by dissolving the material in an organic solvent (C) (hereinafter referred to as component (C)).
As the component (C), any component can be used as long as it can dissolve each component to be used to form a uniform solution, and any one of conventionally known solvents for chemically amplified resists can be used. Two or more types can be appropriately selected and used.
For example, ketones such as γ-butyrolactone, acetone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone, 2-heptanone, ethylene glycol, ethylene glycol monoacetate, diethylene glycol, diethylene glycol monoacetate, propylene glycol, propylene glycol monoacetate, dipropylene glycol Or dipropylene glycol monoacetate monomethyl ether, monoethyl ether, monopropyl ether, monobutyl ether or monophenyl ether and other polyhydric alcohols and derivatives thereof, cyclic ethers such as dioxane, methyl lactate, lactic acid Ethyl, methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methoxypropio Methyl acid, esters such as ethyl ethoxypropionate can be exemplified. These organic solvents may be used independently and may be used as 2 or more types of mixed solvents. The blending ratio of propylene glycol monomethyl ether acetate (PGMEA) and the polar solvent may be appropriately determined in consideration of the compatibility between PGMEA and the polar solvent, preferably 1: 9 to 8: 2, more preferably It is preferable to be in the range of 2: 8 to 5: 5.
More specifically, when ethyl lactate (EL) is blended as a polar solvent, the mass ratio of PGMEA: EL is preferably 2: 8 to 5: 5, more preferably 3: 7 to 4: 6. preferable. In addition, as the organic solvent, a mixed solvent of at least one selected from PGMEA and EL and γ-butyrolactone is also preferable. In this case, the mixing ratio of the former and the latter is preferably 70:30 to 95: 5.
The amount of the component (C) used is not particularly limited, but is a concentration that can be applied to a substrate or the like and is appropriately set according to the coating film pressure. Generally, the solid content concentration of the resist composition is 2 to 2. It is within the range of 20% by mass, preferably 5-15% by mass.

<(D) component>
In the positive resist composition of the present invention, a nitrogen-containing organic compound (D) (hereinafter referred to as “component (D)”) is further added as an optional component in order to improve the resist pattern shape, stability over time and the like. Can be blended.
Since a wide variety of components (D) have already been proposed, any known one may be used, but amines, particularly secondary lower aliphatic amines and tertiary lower aliphatic amines are preferred. .
Here, the lower aliphatic amine refers to an alkyl or alkyl alcohol amine having 5 or less carbon atoms, and examples of the secondary and tertiary amines include trimethylamine, diethylamine, triethylamine, di-n-propylamine, Tri-n-propylamine, tripentylamine, diethanolamine, triethanolamine and the like can be mentioned, and tertiary alkanolamines such as triethanolamine are particularly preferable.
These may be used alone or in combination of two or more.
(D) component is normally used in 0.01-5.0 mass parts with respect to 100 mass parts of (A) component.

<(E) component>
In addition, for the purpose of preventing the deterioration of sensitivity due to the blending with the component (D) and improving the resist pattern shape, retention stability, etc., an organic carboxylic acid or an oxo acid of phosphorus or a derivative thereof (optional) E) (hereinafter referred to as component (E)) can be contained. In addition, (D) component and (E) component can also be used together, and any 1 type can also be used.
As the organic carboxylic acid, for example, malonic acid, citric acid, malic acid, succinic acid, benzoic acid, salicylic acid and the like are suitable.
Phosphorus oxoacids or derivatives thereof include phosphoric acid, phosphoric acid di-n-butyl ester, phosphoric acid diphenyl ester and other phosphoric acid or derivatives thereof such as phosphonic acid, phosphonic acid dimethyl ester, phosphonic acid- Like phosphonic acids such as di-n-butyl ester, phenylphosphonic acid, phosphonic acid diphenyl ester, phosphonic acid dibenzyl ester and derivatives thereof, phosphinic acids such as phosphinic acid, phenylphosphinic acid and their esters Among these, phosphonic acid is particularly preferable.
(E) A component is used in the ratio of 0.01-5.0 mass parts per 100 mass parts of (A) component.

<Other optional components>
The positive resist composition of the present invention further contains miscible additives as desired, for example, additional resins for improving the performance of the resist film, surfactants for improving coating properties, dissolution inhibitors, A plasticizer, a stabilizer, a colorant, an antihalation agent, and the like can be appropriately added and contained.

≪Resist pattern formation method≫
The resist pattern forming method of the present invention can be performed, for example, as follows.
That is, first, the positive resist composition is applied onto a substrate such as a silicon wafer with a spinner or the like, and PAB (pre-baking) is applied for 40 to 120 seconds, preferably 60 to 90 seconds under a temperature condition of 80 to 150 ° C. And a resist film is formed. For this, for example, after ArF excimer laser light is selectively exposed through a desired mask pattern using an ArF exposure apparatus or the like, PEB (post-exposure heating) is preferably performed for 40 to 120 seconds under a temperature condition of 80 to 150 ° C. Is applied for 60-90 seconds. Subsequently, this is developed using an alkali developer, for example, an aqueous solution of 0.1 to 10% by mass of tetramethylammonium hydroxide. In this way, a resist pattern faithful to the mask pattern can be obtained.
An organic or inorganic antireflection film can be provided between the substrate and the coating layer of the resist composition.
The wavelength used for exposure is not particularly limited, and ArF excimer laser, KrF excimer laser, F ₂ excimer laser, EUV (extreme ultraviolet), VUV (vacuum ultraviolet), EB (electron beam), X-ray, soft X-ray Or the like. The resist composition according to the present invention is particularly effective for an ArF excimer laser.

Hereinafter, the present invention will be described in detail with reference to examples.
Synthesis Example 1-1
A mixture of the following monomers (a11), (a21), (a31) and (a41) (0.25 mol) was dissolved in 500 ml of methyl ethyl ketone (MEK), and AIBN (0.01 mol) was added thereto and dissolved. The resulting solution was heated to 65-70 ° C. and this temperature was maintained for 3 hours. Thereafter, the obtained reaction solution was poured into 3 L of well-stirred isopropanol, and the precipitated solid was separated by filtration. The obtained solid was dissolved in 300 ml of MEK, poured into 3 L of well-stirred methanol, the precipitated solid was separated by filtration and dried, and the mass average molecular weight 10000 represented by the following [Chemical Formula 16] The resin 1-1 was obtained.
(A11): 2-methyl-2-adamantyl methacrylate (monomer corresponding to the structural unit in which R is a methyl group and R ¹ is a methyl group in the general formula (1)) 40 mol%
(A21): γ-butyrolactone methacrylate (monomer corresponding to the structural unit in which R is a methyl group in the general formula (10)) 40 mol%
(A31): 3-hydroxy-1-adamantyl methacrylate (monomer corresponding to the structural unit in which R is a methyl group in the general formula (4)) 15 mol%
(A41): Tricyclodecanyl methacrylate (monomer corresponding to the structural unit in which R is a methyl group in the general formula (11)) 5 mol%

（式中、ｐ／ｑ／ｒ／ｓ＝４０／４０／１５／５（モル比））

(Wherein, p / q / r / s = 40/40/15/5 (molar ratio))

Synthesis Example 1-2
Resin 1-2 having a mass average molecular weight of 6900 was obtained by the same composition and method as in Synthesis Example 1-1.

Synthesis Example 2-1
In Synthesis Example 1-1, instead of (a11) and (a21), the following monomers (a12) and (a22) were used, and the composition of each monomer was (a12) / (a22) / (a31) / (a41) = Resin 2-1 having a mass average molecular weight of 10500 represented by the following [Chemical Formula 17] is obtained in the same manner as in Synthesis Example 1-1 except that 40 mol% / 35 mol% / 15 mol% / 10 mol% is used. It was.
(A12): 2-ethyl-2-adamantyl methacrylate (a monomer corresponding to a structural unit in which R is a methyl group and R ¹ is an ethyl group in the general formula (1))
(A22): Norbornane lactone methacrylate (monomer corresponding to the structural unit in which R is a methyl group in the general formula (8))

（式中、ｐ／ｑ／ｒ／ｓ＝４０／３５／１５／１０（モル比））

(Wherein, p / q / r / s = 40/35/15/10 (molar ratio))

Synthesis Example 2-2
Resin 2-2 having a mass average molecular weight of 6400 was obtained by the same composition and method as in Synthesis Example 2-1.

Synthesis Example 3-1
In Synthesis Example 2, a resin 3-1 having a mass average molecular weight of 7200 represented by the following [Chemical Formula 18] is obtained in the same manner as in Synthesis Example 2 except that the following monomer (a23) is used instead of (a22). It was.
(A23): Norbornane lactone methacrylate (monomer corresponding to the structural unit in which R is a methyl group in the general formula (9))

（式中、ｐ／ｑ／ｒ／ｓ＝４０／３５／１５／１０（モル比））

(Wherein, p / q / r / s = 40/35/15/10 (molar ratio))

Synthesis Example 3-2
Resin 3-2 having a mass average molecular weight of 10,000 was obtained by the same composition and method as in Synthesis Example 3-1.

Example 1
In 100 parts by mass of the resin 1-1 having a mass average molecular weight of 10000 obtained in Synthesis Example 1-1, as the component (B), X in the general formula (b-1) is an alkylene group having 3 carbon atoms, A sulfonium compound in which R ^{1 to} R ³ are phenyl groups ([Chemical Formula 19], hereinafter referred to as PAG1) (3.0 parts by mass), (D) component, triethanolamine (0.35 parts by mass), propylene glycol monomethyl ether acetate ( PM) and ethyl lactate (EL) in a mixture (mass ratio 8: 2) to prepare a positive resist composition having a solid content concentration of 8% by mass.

Next, an organic antireflection film composition “ARC-29A” (trade name, manufactured by Brewer Science Co., Ltd.) is applied onto a silicon wafer using a spinner, and baked on a hot plate at 215 ° C. for 60 seconds to be dried. Thereby, an organic antireflection film having a thickness of 77 nm was formed. Then, the positive resist composition is applied on the antireflection film using a spinner, prebaked (PAB) at 120 ° C. for 90 seconds on a hot plate, and dried to form a resist layer having a thickness of 250 nm. did.
Next, an ArF excimer laser (193 nm) is selectively passed through a mask pattern (binary) using an ArF exposure apparatus NSR-S302 (manufactured by Nikon; NA (numerical aperture) = 0.60, σ = 0.55). Irradiated.
Then, PEB treatment was performed at 130 ° C. for 90 seconds, and further paddle development was performed at 23 ° C. with a 2.38 mass% tetramethylammonium hydroxide aqueous solution for 60 seconds, followed by washing with water for 20 seconds and drying to form a resist pattern. Formed.

As a result, using the positive resist composition of Example 1, the exposure amount Eop (sensitivity) at which a mask with a width and width of 120 nm and a 1:10 (1320 nm pitch (P)) mask is transferred to a space width of 80 nm is obtained. It was 25 mJ / cm ² .
Further, the formed isolated resist pattern having a width of 80 nm had a highly rectangular shape with the top shape not rounded, the resist line sidewalls being vertical.
Further, 3σ, which is a scale indicating the LER of the pattern formed above, was obtained. As a result, 3σ of the obtained pattern was 5.0 nm. In addition, 3σ is a triple value of the standard deviation (σ) calculated from the result of measuring the width of the resist pattern of the sample at 32 locations with a side length SEM (trade name “S-9220” manufactured by Hitachi, Ltd.). (3σ). This 3σ means that the smaller the value, the smaller the roughness and the uniform width resist pattern was obtained.
The depth of focus (DOF) was 450 nm.

  Further, the line-and-space separation / resolving power when the exposure was performed while the mask pitch was gradually reduced at the exposure amount Eop was a 240 nm pitch. It shows that the smaller the value of the separation resolution, the better the performance as a resist composition. This evaluation method is frequently used by those skilled in the art.

Examples 2-18, Comparative Examples 1-5
A positive resist composition was prepared in the same manner as in Example 1 except that the type of component (A) and the type and amount (parts by mass) of component (B) were changed as shown in Table 1.
In Examples 9 to 12 and Comparative Example 3, the temperature of PAB in Example 1 was changed to 105 ° C., and the temperature of PEB was changed to 95 ° C. In Examples 13 to 18 and Comparative Examples 4 to 5, the temperature of PAB in Example 1 was changed to 125 ° C., and the temperature of PEB was changed to 115 ° C.

  In Table 1, PAG2 is a compound represented by the following [Chemical Formula 20], PAG3 is a compound represented by the following [Chemical Formula 21], and PAG4 is a compound represented by the following [Chemical Formula 22].

The positive resist compositions prepared in Examples 2 to 18 and Comparative Examples 1 to 5 were evaluated in the same manner as in Example 1, and the results are also shown in Table 1.
In Table 1, “Round” indicates that the top shape of the resist sidewall in the space portion near the surface of the resist film is rounded, and the shape of the space portion is tapered.

As is clear from the above results, the positive resist compositions of Examples 1 to 18 had high resolution of isolated space patterns and L & S patterns. Furthermore, it was found that the shape of the formed pattern was good, the LER was small, and the DOF was large. Especially, the positive resist compositions of Examples 13 to 18 using the resin 3 were particularly excellent in LER.

Claims (16)

(A) a positive resist composition containing a resin component whose alkali solubility is increased by the action of an acid, and (B) an acid generator component which generates an acid upon exposure,
The resin component (A) contains a structural unit (a1) derived from a (meth) acrylic acid ester containing a polycyclic group-containing acid dissociable, dissolution inhibiting group, a lactone-containing monocyclic or polycyclic group (meta ) Other than the structural unit (a2) derived from an acrylate ester, the structural unit (a3) derived from a (meth) acrylate ester containing a hydroxyl group-containing polycyclic group, and the structural units (a2) and (a3) A copolymer containing a structural unit (a4) derived from a (meth) acrylic acid ester containing a polycyclic group-containing non-acid dissociable, dissolution inhibiting group,
The acid generator component (B) is represented by the following general formula (b-1) or (b-2)

[Wherein X represents an alkylene group having 2 to 6 carbon atoms in which at least one hydrogen atom is substituted with a fluorine atom; Y and Z each independently represents at least one hydrogen atom substituted with a fluorine atom; R ^{1 to} R ³ each independently represents an aryl group or an alkyl group, and at least one of R ^{1 to} R ³ represents an aryl group]
A positive resist composition comprising at least one sulfonium compound represented by the formula: The structural unit (a1) is represented by the following general formula (1), (2) or (3)

(Wherein R is a hydrogen atom or a lower alkyl group, and R ¹ is a lower alkyl group)

(Wherein R is a hydrogen atom or a lower alkyl group, and R ² and R ³ are each independently a lower alkyl group)

(Wherein R is a hydrogen atom or a lower alkyl group, and R ⁴ is a tertiary alkyl group)
The positive resist composition according to claim 1, which is at least one structural unit represented by the formula: The positive resist composition according to claim 2, wherein the structural unit (a1) is a structural unit represented by the general formula (1), and R ¹ in the general formula (1) is a methyl group or an ethyl group. Stuff.   The positive resist composition according to claim 1, wherein the structural unit (a2) is a structural unit derived from a (meth) acrylic acid ester containing a lactone-containing monocycloalkyl group or bicycloalkyl group. .   The positive resist composition according to claim 4, wherein the structural unit (a2) is a structural unit derived from a (meth) acrylic ester of γ-butyrolactone.   The positive resist composition according to claim 4, wherein the structural unit (a2) is a structural unit derived from a (meth) acrylic ester of norbornane lactone. The structural unit (a2) is represented by the following general formula (9).

(Wherein R is a hydrogen atom or a lower alkyl group)
The positive resist composition according to claim 6, which is a structural unit represented by:   The positive resist composition according to claim 1, wherein the structural unit (a3) is a structural unit derived from a (meth) acrylic acid ester containing a hydroxyl group-containing adamantyl group. The structural unit (a3) is represented by the following general formula (4).

(Wherein R is a hydrogen atom or a lower alkyl group)
The positive resist composition according to claim 8, which is a structural unit represented by:   The structural unit (a4) is a structural unit derived from at least one selected from tricyclodecanyl (meth) acrylate, adamantyl (meth) acrylate, and tetracyclododecanyl (meth) acrylate. The positive resist composition according to any one of the above. The structural unit (a4) is represented by the following general formula (11).

(Wherein R is a hydrogen atom or a lower alkyl group)
The positive resist composition according to claim 10, which is a structural unit represented by:   The positive resist composition according to claim 1, wherein the resin component (A) has a mass average molecular weight of 7500 or less.   The proportion of the structural units (a1) to (a4) in the resin component (A) is such that the structural unit (a1) is in the range of 25 to 50 mol% and the structural unit (a2) is in the range of 25 to 50 mol%. The positive resist composition according to claim 1, wherein the structural unit (a3) is in the range of 10 to 30 mol% and the structural unit (a4) is in the range of 3 to 25 mol%. Stuff.   The acid generator component (B) further contains an onium salt acid generator having a linear fluorinated alkylsulfonate ion having 1 to 7 carbon atoms as an anion. A positive resist composition.   Furthermore, the positive resist composition in any one of Claims 1-14 containing a nitrogen-containing organic compound. A resist film is formed on a substrate using the positive resist composition according to claim 1, the resist film is selectively exposed, and then alkali-developed to form a resist pattern Forming a resist pattern.